The invention relates to a brake apparatus for a vehicle that switches feedback control into feed forward control and thus continues rotation control when a motor rotation number cannot be detected due to any cause during the feedback control of the motor rotation number and thus the feedback control cannot be performed.
For example, JP-A-2006-21745 discloses a brake apparatus for a vehicle having a fluid pressure brake apparatus and a regenerative brake device. The fluid pressure brake apparatus generates a basic fluid pressure corresponding to a brake operation by a master cylinder, and applies the generated basic fluid pressure to wheel cylinders of the respective wheels connected by an oil path having the master cylinder and a fluid pressure control valve, thereby generating a basic fluid pressure braking force for each wheel. The fluid pressure brake apparatus drives an electric motor in response to a control fluid pressure command value to thus drive a fluid pressure pump provided to the fluid pressure control valve and to thus generate a control fluid pressure and applies the generated control fluid pressure to the wheel cylinders, thereby generating a control fluid pressure braking force for each wheel. The regenerative brake device generates a regenerative braking force corresponding to a brake operating state for any one of the wheels.
In the brake apparatus for a vehicle, when the regenerative braking force varies in response to a driver-request braking force and thus proves deficient, the deficiency of the regenerative braking force is compensated by the control fluid pressure braking force. That is, the electric motor is driven at high rotation number to thus increase a discharge flow rate of a fluid pressure pump and a brake fluid having an unnecessary flow rate part regarding a necessary flow rate part is made to escape from the fluid pressure control valve to the master cylinder, thereby adjusting the control fluid pressure. According to the above brake apparatus for a vehicle, it is possible to cope with a situation where the regenerative braking force proves deficient with respect to the request braking force, with good responsiveness, as required.
JP-A-10-119748 discloses a brake apparatus for a vehicle having a device that controls a motor rotation number to thus change a discharge flow rate of a pump and thus controls a control fluid pressure. According to this brake apparatus for a vehicle, when it is required to increase flow rate consumption of a brake fluid pressure due to an operation of rapidly pedaling a brake, it is possible to enhance the responsiveness by increasing the motor rotation number to thereby increase the discharge flow rate of the pump.
In the brake apparatus for a vehicle having the fluid pressure brake apparatus and the regenerative brake device, the durability of the electric motor, which drives the fluid pressure pump for generating the control fluid pressure frequently operating in a brake region, is important. According to the brake apparatus for a vehicle disclosed in JP-A-2006-21745, the electric motor should be driven at a high rotation number, so that the lifespan of the electric motor may end at an early stage. According to the brake apparatus for a vehicle disclosed in JP-A-10-119748, since the motor rotation number is controlled so as to change the discharge flow rate of the pump, it is possible to increase the durability of the electric motor. However, since the pedaling degree of the brake pedal varies every moment, the load to be applied to the fluid pressure pump is also varied. Regarding this, it is not suggested how to control the motor rotation number in this situation.
Regarding the motor, it is effective to decrease a rotation number thereof so as to enhance the lifespan. Regarding this, JP-A-10-119748 suggests feedback (FB) control of detecting a motor rotation number and thus appropriately correcting a voltage to be applied to a motor. The feedback control is performed so that a detected motor rotation number is the same as a target rotation number of the FB control. Although not described in JP-A-10-119748, when a motor rotation number cannot be detected due to any cause and the feedback control cannot be thus performed, it is considered that the feedback control is switched into feed forward (FF) control and thus the rotation control is continuously performed. At this time, a target rotation number of the FF control is set to be higher than the target rotation number of the FB control so that a braking force of wheels does not prove deficient due to the insufficient rotation number even when an estimated rotation number has an estimated error. Hence, when the control is switched from the feedback control to the feed forward control, a command value of the motor rotation number is abruptly increased to the target rotation number of the FF control, as shown with an arrow r1 in FIG. 17B. When a control current (which is indicated by an arrow i1 in FIG. 17C) of a fluid pressure control valve connected between a master cylinder and a wheel cylinder is suddenly decreased so as to follow the increased motor rotation number, the fluid pressure control valve is abruptly opened. However, the motor rotates with the target rotation number of the FF control in accordance with a time constant thereof and a pumping flow rate of a pump does not abruptly follow even when the motor reaches the target rotation number of the FF control. Thus, since a brake fluid having a flow rate larger than ever is relieved from the abruptly opened fluid pressure control valve, a fluid pressure of the wheel cylinder is abruptly decreased, as shown with a curve wc1 in FIG. 17D.
Like this, when the control is switched from the feedback control to the feed forward control, a difference is caused between the pumping flow rate of the pump and a degree of opening of the fluid pressure control valve. Thereby, the brake fluid pressure of the wheel cylinder is not smoothly changed, so that a driver feels uncomfortable upon a brake operation.